[unreadable] Direct intra myocardial injection may permit local delivery of protein and gene therapy agents for myocardial and coronary artery disease. However, little is known about the immediate fate of materials administered via percutaneous endomyocardial catheters or via surgical epicardial injection. Unrecognized loss of injected material can negatively influence the outcome of a preclinical trial. Both pharmaceutical developers have long privately discussed this problem and developers of drug delivery systems. A recent publication demonstrates that myocardial retention of injected material can vary greatly. We hypothesize that a commercial reagent can be developed to provide both detection and quantitation of cardiac drug delivery systems in vivo models, as well as provide the means to uniquely identify experimental subgroups during double blind animal trials. In addition, this reagent can be used as a teaching tool and as a means to certify clinicians in myocardial injection techniques. Our Phase I application seeks support to develop a set of reagents, co-labeled with both a stable isotope and a fluorescent marker. Our proposed reagent will allow validation of cardiac injection methods, allow monitoring of technical competence during preclinical trails, allow identification of subject groups, and assure higher quality of in vivo data. [unreadable] [unreadable]